Nickel and rare earth metal containing catalysts have been widely used commercially to make polybutadiene (BR) in solution and slurry polymerizations. Commercial facilities employ solution and slurry processes which are energy intensive. These processes produce polymer in a bale-like form which must be subsequently pulverized or ground.
More recently, it has been discovered that polydienes such as polybutadiene and polyisoprene can be produced in gas phase, e.g., fluidized bed, reactors. Such processes are described, for example, in U.S. Pat. Nos. 4,994,534 and 5,453,471; and in WO 96/04322 and 96/04323. These processes operate at lower cost as compared to solution and slurry processes and produce a polymer which is granular and flowable upon leaving the gas phase reactor. The polymer does not require subsequent pulverization steps. The gas phase production is also more environmentally acceptable due to the absence of a solvent removal step.
Compared to rare earth metal catalysts, such as neodymium metal containing catalysts, nickel catalysts are inexpensive and readily available. However, nickel catalysts which are sometimes employed to produce polybutadiene and polyisoprene in solution and slurry processes have not been sufficiently active for the production of these polymers in gas phase, fluidized reactions. They can have long induction periods and short life spans for producing polymer, and can produce a product such as polybutadiene having less desirable levels of 1,4-cis butadiene units (i.e., less than 90%).
Accordingly, there is a need to increase the productivity of these nickel catalysts such that they can be used cost-effectively in gas phase reactions.